Measurement of the polarized structure function sigma(LT ') for pion electroproduction in the Roper-resonance region

The polarized longitudinal-transverse structure function {sigma}{sub LT{sup '}} measures the interference between real and imaginary amplitudes in pion electroproduction and can be used to probe the coupling between resonant and nonresonant processes. We report new measurements of {sigma}{sub LT{sup '}} in the N(1440)(1/2){sup +} (Roper) resonance region at Q{sup 2}=0.40 and 0.65GeV{sup 2} for both the {pi}{sup 0}p and {pi}{sup +}n channels. The experiment was performed at Jefferson Lab with the CEBAF Large Acceptance Spectrometer (CLAS) using longitudinally polarized electrons at a beam energy of 1.515 GeV. Complete angular distributions were obtained and are compared to recent phenomenological models. The {sigma}{sub LT{sup '}}({pi}{sup +}n) channel shows a large sensitivity to the Roper-resonance multipoles M{sub 1-} and S{sub 1-} and provides new constraints on models of resonance formation.